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Subject: Re: [PATCH] mm: Define VM_(MAX|MIN)_READAHEAD via sizes.h constants
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-mm@kvack.org, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-afs@lists.infradead.org,
        linux-fsdevel@vger.kernel.org
References: <20181221125314.5177-1-nborisov@suse.com>
 <20181221132423.GA10600@bombadil.infradead.org>
From:   Nikolay Borisov <nborisov@suse.com>
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Date:   Fri, 21 Dec 2018 16:06:42 +0200
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On 21.12.18 г. 15:24 ч., Matthew Wilcox wrote:
> On Fri, Dec 21, 2018 at 02:53:14PM +0200, Nikolay Borisov wrote:
>> All users of the aformentioned macros convert them to kbytes by
>> multplying. Instead, directly define the macros via the aptly named
>> SZ_16K/SZ_128K ones. Also remove the now redundant comments explaining
>> that VM_* are defined in kbytes it's obvious. No functional changes.
> 
> Actually, all users of these constants convert them to pages!
> 
>> +	q->backing_dev_info->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
>> +		sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
>> +	sb->s_bdi->ra_pages	= VM_MAX_READAHEAD / PAGE_SIZE;
>> +	sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
>> +	sb->s_bdi->ra_pages = VM_MAX_READAHEAD / PAGE_SIZE;
> 
>> -#define VM_MAX_READAHEAD	128	/* kbytes */
>> -#define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
>> +#define VM_MAX_READAHEAD	SZ_128K
>> +#define VM_MIN_READAHEAD	SZ_16K	/* includes current page */
> 
> So perhaps:
> 
> #define VM_MAX_READAHEAD	(SZ_128K / PAGE_SIZE)
> 
> VM_MIN_READAHEAD isn't used, so just delete it?

I thought about that but didn't know if people will complain that some
times in the future we might need it.

>